We recently upgraded our pacifier clips to have a MUCH better hold so it stays in place regardless of how much baby pulls on it. This makes them slightly more complicated to open, but once you figure it out, it is really no problem.
Push up on the white square tab with your thumb. At the same time, pull teeth apart with your other hand. After you have opened it once, it will be very easy to open it with one hand. It just takes opening it the first time to know the amount of pressure it takes.
It may flex and seem like it is going to break, but it won't. Watch the video below to see how to easily open the Ike and Leo Pacifier Clip.